Short Term Reproducibility in Apparent Diffusion Coefficient for Diffusion Weighted MRI of the Prostate

Purpose:In this study we evaluate the short term reproducibility of Diffusion Weighted MR Imaging (DW-MRI) of the prostate by analyzing variation in ADC maps.

Methods:14 patients with biopsy proven prostate cancer were evaluated under an IRB-approved protocol. Each patient underwent two, identical DW-MRI scans with the patient remaining on the table and only automatic shimming with tuning and matching between acquisitions. ADC maps were generated using a least squares fit. The prostate and ROIs within cancer lesions were delineated on each scan per patient by two radiologists using the b-0 images and a rigid local registration was performed using multiple radiologist-defined landmarks throughout the prostate on each of the two scans. The absolute and percentage differences in ADC per voxel were calculated. For each patient the prostate was divided into equally spaced sextants and the voxel-based variation in each sextant was compared.

Results:The absolute difference in ADC per voxel within the prostate ranged from 1.13x10⁻⁹ to 1.91x10⁻³ mm²/sec (mean and standard deviation percentage difference 10.35% ± 10.91%). The largest variation is seen in the posterior apex (mean 11.46%, median 8.02%, standard deviation 11.73%) although we were not able to demonstrate statistical significance in the difference in variation between sextants. Cancer ROIs showed a mean, median and standard deviation in ADC difference of 13.36%, 6.90% and 14.48%, respectively.

Conclusion:DW-MRI has strong potential to become a powerful quantitative imaging biomarker for prostate cancer. It is imperative to know the reproducibility of the imaging method when utilizing DW-MRI in the clinic or developing new approaches for its use. Our data demonstrates that ADC variation within the prostate is modest, on the order of 10%, similar to other abdominal tissues, and the variation appears to be highest in the apex region of the prostate.